[redmodelt]

If you got the new caps they only fit the newer rearends. What year are you working on?
I put the taper down to the inside.
Correction 1915 rear ends would use the smaller ID cap. As Steve said, replacement caps will need to be shimmed. Or you could do an old time fix, cut 4 - 6 slots maybe 1/2 way down the side and use a hose clamp to hold it in place.